A textured dual-sided sheet of ePTFE, as in my U.S. Pat. Nos. 5,282,856 and 6,921,418, has multiple uses as an implant in surgical reconstruction of the body. It has applicability as a fitted covering for space-occupying implants that require isolation and stabilization such as implanted infusion pumps, orthopedic devices, electronic devices such as defibrillators, glucose meters, pacemakers, and others. It also finds applicability as a hernia repair material, as a safe hypoallergenic dura mater replacement material, as supportive coverings for soft organs such as kidney, pancreas, liver or spleen, for example. It is also useful as a protective support and drainage cover for breast and other soft implants. Additionally, it is useful as a repair material for wall of thorax, ruptured diaphragm, pericardium, and so forth.
Used as an implanted covering, the textured dual-sided ePTFE sheet structure is very useful for its ability to induce bio-integrative scar on its textured surface, thus enabling it to become quickly and permanently attached to adjacent bodily structures. A textured dual-sided ePTFE tubular structure is another useful implantable structure that benefits from the ability to bio-integate with the body. Drugs, transplanted live tissues in their nutrient media including: pancreatic beta cells, bone marrow, stem cells, and others contained within such a textured sheet or tubular repository structure can serve as in situ reservoirs upon healing.
Bio-integration implies an intense adherence between an implanted material and the body, which can help defeat potential complications of surgery such as de-lamination, dehiscence and seroma fluid accumulation. The avidity of bio-integative scar attachment is principally characterized as the amount of force required to physically separate the tubular ePTFE structure from attached soft tissue under standardized test conditions.
Whereas smooth ePTFE surfaces with porosities in the 1-2 micron range are used to prevent adherence to bodily structures, the purpose of micro-textured ePTFE is to do the opposite—to induce targeted bio-integrative scar and adherence. Creating both smooth and micro-textured surfaces on the same implantable ePTFE structure is a manufacturing challenge. Crafting both surfaces on a tubular ePTFE structure adds another degree of complexity. In order to attract fibroblasts, textured ePTFE surfaces must be free of oxidized by-products and other surface contaminants such as manufacturing debris, glazing, or extrusion impressions.
According to Goldfarb (U.S. Pat. No. 6,436,135), by providing the appropriate wall thickness of the textured tubular structure, as well as by creating through and through holes or slits of optimal diameter and density, a highly desirable neo-intima cell layer can be encouraged and supported with capillary in-growth into the lumen. It discloses a prosthetic vascular device formed from a small bore tube of polytetrafluoroethylene which has been heated, expanded and sintered so as to have a microscopic superstructure of uniformly distributed nodes interconnected by fibrils and characterized by: (a) an average internodular distance which is (i) large enough to allow transmural migration of typical red cells and fibroblast, and (ii) small enough to inhibit both transmural blood flow at normal pressures and excessive tissue ingrowth; and (b) an average wall thickness which is (i) small enough to provide proper mechanical conformity to adjacent cardiovascular structures, and (ii) large enough, when taken in conjunction with the associated internodular distance, to prevent leakage and excess tissue ingrowth, to allow free and uniform transmural nutrient flow, and to assure mechanical strength and ease of implantation.
According to Zukowski (U.S. Pat. No. 5,462,781) entitled “Surface Modified Porous Expanded Polytetrafluoroethylene and Process for Making”, an implantable porous expanded polytetrafluoroethylene material has a microstructure of nodes interconnected by fibrils and the surface of the material has been modified by the removal of fibrils from the surface. The surface has the appearance of freestanding node portions not interconnected by fibrils but rather having open valleys disposed between the freestanding node portions. Unmodified material beneath the surface maintains the original microstructure of nodes interconnected by fibrils. The modification is preferably done by exposing the surface to radio frequency gas plasma discharge with a reactive etching gas for a lengthy amount of time such as about ten minutes. The depth of fibril removal from the surface is substantially a function of the duration and amount of energy applied to the surface.
According to Gore (U.S. Pat. No. 4,187,390) entitled “Porous products and process therefore”, a tetrafluoroethylene polymer in a porous form has an amorphous content exceeding about 5% and has a micro-structure characterized by nodes interconnected by fibrils. The material is said to have high porosity and high strength. Shaped articles such as films, tubes, rods, and continuous filaments are contemplated. Laminations can be employed and impregnation and bonding can be used.
Historically, severe scar contracture around a silicone breast implant would harden and deform the entire breast, with consequences for both patient and surgeon. Multiple causes of scar contracture have been identified, including a ready supply of seroma fluid containing collagen monomers, cellular debris, mediators of inflammation due to surgical injury, physical abrasion and exposure to allergenic materials like silicone gel, and wound contaminants. In the case of wounds containing soft implants, seroma fluid containing collagen monomers and admixed mediators of inflammation are problematic because such a combination promotes additive layers of scar. A large amount of fluid permits an implant to float in the wound space and allows for mechanical abrasion as it makes repeated abrasive contact with surrounding soft tissues, and thus can become a serious complication of surgery. So-called developing “capsular scar contractures” become thicker and more dense and grossly distort an implant and surrounding breast tissue.
Over time, a number of partial solutions to the problem of scar contractures have been tried including: (1) more cohesive gel fillers for implants which are less likely to be allergenic and more likely to retain implant shape, (2) sub-muscular rather than sub-glandular placement of implants, (3) non-allergenic fillers such as normal saline, (4) pressure adaptive implants, (5) fastidious surgical dissection technique with frequent wound irrigation and suction, (6) use of cortico-steroid injections into surrounding soft tissues, and (7) topography-modifying implant surfaces, as well as others.
However, significant esthetic problems of sub-optimal implant position, implant deformation and hardness remain for some patients, often necessitating re-operation plus installing a new set of implants. Implant motion and abrasion injury at the interface with soft tissue results in accumulation of seroma fluid in the wound. Such seroma fluid accumulation which contains cellular debris, mediators of inflammation, fibroblasts and collagen, remains an un-solved problem requiring a solution. Because it can persist for a prolonged period of time in a wound space as an inflammatory material, it promotes the development of multiple layers of capsular scar. Such capsular scar can then undergo severe contraction to deform the entire breast.